The invention is directed to a carbon dioxide gas scavenger-based material for use in packaging of coffee, fresh produce and the like. More particularly, there is disclosed a carbon dioxide scavenging layer for use as the interior layer of a package or container which includes at least one composite carbon dioxide absorbent or carbon dioxide scavenging filler material dispersed into a polymeric matrix.
Many food products such as roasted coffee, fresh produce, or the like, generate significant amounts of carbon dioxide after being packaged. This gas can lead to pressure buildups in the package resulting in: bulging; rupture; loss of freshness; poor shelf appearance; and increased anaerobic bacterial activity.
Traditionally, several approaches have been used to remove the carbon dioxide gas from the inside of a package. In one approach, as in the case of fresh produce, micro perforated films are used. These films allow the gaseous exchange of the carbon dioxide and the oxygen between the inside and the outside of the package thus allowing it to respire. These micro perforated films are expensive and cannot be used to package coffee which is sensitive to the effects of oxygen and moisture. Another type of approach has been used in the case of roasted coffee. A one way gas venting valve has been added to the package. These types of one way gas venting valves open when the carbon dioxide pressure inside the package exceeds the outside pressure and thereby vents out the excess carbon dioxide. These valves are relatively expensive, require separate expensive equipment to install, can slow production rates, and increase machine set up and down time. The valves also vent the aroma, which can affect the flavor and quality of the brewed coffee, along with the carbon dioxide to the atmosphere. Further, as the valve operates by the pressure difference between the inside and outside package, its performance can be affected by altitude.
In yet another approach, the carbon dioxide inside the package is reduced by sachets containing a scavenger material, such as an alkaline earth metallic oxide, or hydroxide that can selectively react with the carbon dioxide in the package. The sachets are relatively expensive, add an extra step to the filling process, and pose potential risks such as accidental grinding, rupture and ingestion.
U.S. Pat. No. 4,552,767, Saleeb et al, discloses a combination of calcium hydroxide and sodium or potassium hydroxide to be used as a carbon dioxide scavenger in coffee packaging. The patent relates to the use of an envelope or bag to contain the active ingredients (sachet). The preferred method attaches the sachet to the inside wall of the flexible package by heat sealing or gluing. The active components are not disposed in the polymer matrix and must be added as a separate step in the filling process.
International Application (WO 98/31542) discloses a packaging laminate with a CO2 and O2 scavenging core layer consisting of Ca(OH)2 or CaO and low density polyethylene (LDPE). However, there is no mention of the scavenging rate or scavenging efficiency of the system. Normally the rate of CO2 scavenging by Ca(OH)2 or CaO or mixtures of both is very low under the dry environment. At a low relative humidity (RH) such as 25%, the reaction rate is very slow. In order to speed up the CO2 scavenging rate, one has to maintain a high RH (for instance, 90%) in the packaging environments. In the case of storing dry food such as roasted coffee beans, the rate is too slow to effectively remove the CO2 gas released from the roasted beans.
The present invention deals with an integrated CO2 scavenging system, with an extremely fast rate of CO2 reduction and a very high efficiency, by incorporating into a resin or resins using the usual compounding techniques: 1) CO2 scavenging fillers such as alkaline earth metal hydroxides, alkaline earth metal oxides, alkali metal hydroxides, alkali metal oxides, or their mixtures, and 2) moisture producing/retaining agents or moisture retaining agents. The composite carbon dioxide scavenger filler is a combination of CO2 scavenging filler and moisture producing/retaining agent or moisture retaining agent. The moisture producing/retaining agents include alkali metal hydroxides such as NaOH, KOH and alkali metal oxides such as Na2O. The moisture retaining agents include, but are not limited to, hygroscopic desiccant materials such as silica gel, bentonite clay, NaCl, CaCl2, attapulgite clay, magnesium sulfate, etc.
When the moisture retaining agents are incorporated into the resin along with the CO2 scavenging fillers, one needs to condition the resin blends in high RH environments for a period of time so that the moisture retaining agents can absorb the moisture until they reach the point of saturation. Such an environment can be provided by steam treatment on line or off line and humidity chambers off line. The moisture kept within the moisture retaining agents can then speed up the CO2 scavenging reaction.
When the moisture producing/retaining agent is used, water is generated by reaction with CO2:
alkali metal hydroxide+CO2xe2x86x92alkali metal carbonate+H2Oxe2x80x83xe2x80x83(1)
Since the alkali metal hydroxides are also hygroscopic and deliquescent, the water produced by the above reaction is also retained in the system and thus speeds up the CO2 scavenging rate. Another unique feature of these moisture producing/retaining agents is that they strongly absorb the moisture in the environments even at a very dry condition. For example, NaOH will keep absorbing the moisture from the environments until the relative humidity of the environments reach around 6% or below. Thus, no additional pre-conditioning is required when the moisture producing/retaining agent is used in the system. Similarly, alkali metal oxide, being hygroscopic and deliquescent, will absorb moisture and react to produce alkali metal hydroxide:
alkali metal oxide+H2Oxe2x86x92alkali metal hydroxidexe2x80x83xe2x80x83(2)
The alkali metal hydroxide will then react with CO2 to produce water, as shown in Equation (1).
As far as the scavenging reaction of alkaline earth metal hydroxide and alkaline earth metal oxide, the following reactions, for example, can take place:
Mg(OH)2+CO2-xe2x86x92MgCO3+H2Oxe2x80x83xe2x80x83(3)
and
CaO+H2Oxe2x86x92Ca(OH)2xe2x80x83xe2x80x83(4)
Ca(OH)2+CO2xe2x86x92CaCO3+H2Oxe2x80x83xe2x80x83(5)
The CO2 scavenging reactions by alkaline earth metal hydroxide or alkaline earth metal oxide, as shown in Equation 3 through 5, require a humid environment in order to achieve a reasonable reaction rate. The addition of moisture producing/retaining agents or moisture retaining agents into these alkaline earth metal hydroxide or oxide will dramatically increase the scavenging rates.
It is an objective of the present invention to provide a cost effective, safe, and unique way to remove the carbon dioxide from the inside of a coffee package, or container.
It is a further objective of the invention to integrate the composite carbon dioxide absorbent scavenger material into the interior wall of a package or container itself.
It is a further objective of the invention to incorporate the composite carbon dioxide absorbent scavenger material into the wall of a package, as part of a blend, in the layer in direct contact with the carbon dioxide from the coffee or adjacent to a functional heat seal layer with the desired diffusion properties.
It is an objective of the invention to make the composite carbon dioxide scavenger material integral with the package without the need for installation and/or insertion operations, as used in the case of degassing valves, or sachets.
It is a further objective of the invention to utilize a metal hydroxide, or oxide, or mixtures thereof, in combination with a moisture producing/retaining agent or moisture retaining agent, as a composite scavenger that can absorb and/or react with high levels of carbon dioxide rapidly and efficiently.
It is a further objective of the invention to increase the surface area of the product contact scavenging layer and therefore the efficiency of the scavenger material by modifying a package, such as by using a corrugated coated film or corrugating the whole multilayer coated package structure, or by designing ribs or gussets in the package.
A cost effective, safe and unique way to remove carbon dioxide from the inside of a coffee package is to integrate a composite carbon dioxide absorbent scavenger material into the walls or directly into a layer of the package itself. This can be done by coating the layer as a blend, as the layer in contact with the carbon dioxide from the coffee. The scavenger layer becomes part of a multilayer structure, which also includes if desired, moisture and oxygen barrier materials. The absorbent scavenger material, which is blended into a polymeric matrix, can also be coated onto the inner side of a substrate. The scavenger compound can also be made directly into a blown or cast film, either as an individual layer of a multilayer coated extruded film or as a monolayer film on its own. A high level of carbon dioxide absorption requires a high percentage of the scavenger absorbent filler in the coated blend. This can be achieved by compounding various percentages of an absorbent such as calcium hydroxide, or calcium oxide, or other metal hydroxides, or oxides, in a polymeric matrix resin such as a low density polyethylene, or the like. A moisture producing/retaining or moisture retaining agent is also added into the scavenger filler (forming the composite CO2 scavenging filler) to ensure a fast and complete reaction with CO2. The scavenging blend can be produced using a twin-screw extruder, or a single screw extruder equipped with the mixing elements, or a single screw kneader, or an internal mixer such as a Banbury mixer. Along with the composite filler and polymer matrix, a preferred compatabilizer is added to enable one to achieve good dispersion and mixing at high levels of the filler. Due to the basic nature of the carbon dioxide scavenging fillers, care is taken not to use very strong mixing elements in the screws to protect the polymer elements. If desired, antioxidants can be added into blends to reduce the extent of degradation to the resins. The particle size of the filler also can affect the compounding and the absorption. Agglomeration of particles can reduce efficiency of the scavenger performance. The moisture content of the composite scavenger filler as well as the polymer can have an effect on the dispersion of the filler particles. Drying of the composite scavenger fillers or polymers may be necessary in some cases to reduce the moisture contents in order to obtain a homogeneous mixture of the blends. The carbon dioxide scavenging is a surface effect, and hence the larger the area of the coated surface, the greater the amount of the carbon dioxide absorbed by, and/or reacted with the scavenger.